Light Reflection and Refraction

Imagine a situation where you look into a pond. You see lily pads and your own reflection in the water. Pretend you just dropped a rock into the water. Now proceed to pick the rock up by sticking your hand in the water. Do you ever wonder why your hand appears to 'bend' in the water? Well, I stuck my hand in a fairly clear pond once to pick up a rock and I thought I saw my hand bending, but after consulting my Physics book, I realized the 'bending' I saw occurred because light refracts or bends in water.

I tried sticking several other things into the water to see what would happen. I put a stick in the water, rocks, leaves, and finally my hand, again. Every time I put something in the water, I sat looking from directly above or slightly from the side. No matter what I put in the pond, everything seemed to bend. I didn't put a flashlight in and try to shine the light back towards me. All the objects I placed in the water don't conduct their own light source, so I knew I didn't unknowingly redirect the light. I didn't cause the bending, but the light going from one transparent medium to another (obliquely) did.

Light bends when light changes speed and travels in an oblique line from one medium to another. Some objects generate light and some don't. Stars create light, while my hand does not. My hand is not luminous, meaning my hand doesn't generate its own light source, but instead my hand reflects light.

Reflecting light means light bounces off an object, like my hand, and enters my eyes where I can interpret the image. Light will generally travel in a straight line (the shortest distance between two points), except when light enters water from the air. Light always wants to take the most efficient path requiring the least amount of time, according to Fermat's principle of least time. As light travels through different mediums, or objects, the actual speed of light will vary. The light travels faster in the air, so light slows down upon entering water.

In short, the natural phenomena I observed definitely made me wonder why every thing kept bending. I soon learned the light simply refracted and reflected off of my hand and generated the bending I observed. Refraction is the process by which an oblique ray of light travels from one transparent medium to another, due to the differing speeds light takes when traveling through different medias. Light reflection occurs when light bounces off an object in the same angle light hits the object. You can think of rays of light reflection in another way: the angle of approach equals the angle of departure.

Source: Conceptual Physics 8^th Edition. Paul G. Hewitt. Addison-Wesley. Book.